1. Field of the Invention
The present invention relates to an organic electroluminescent (EL) light emitting device and a liquid crystal display using the same. More particularly, the present invention relates to an organic EL light emitting device emitting polarized light and a liquid crystal display using the same.
2. Description of the Related Art
In recent years, liquid crystal displays (LSDs) have been used, in place of CRTs, in various fields including T.V. sets, personal computers and personal digital assistants (PDAs). As displays, plasma displays, organic EL displays, inorganic EL displays and the like have also received attention, and commercialization of these displays is now under way.
Among others, organic EL displays, which can emit light spontaneously and use a thin film, are expected as promising light and thin displays. Moreover, great progress has been made in development of materials lately. Actually, a material capable of emitting three colors of blue, green and red efficiently has been developed.
A liquid crystal display using an organic EL light emitting device as the backlight has been proposed in Japanese Laid-Open Patent Publication Nos. 61-153693 and 62-227121, for example. Also, Japanese Laid-Open Patent Publication No. 11-316376 discloses use of an organic EL light emitting device emitting polarized light as the backlight to thereby omit one polarizer of a liquid crystal display, and discusses that this can not only reduce power consumption but also improve the light use efficiency.
The emission polarization ratio of the conventional organic EL light emitting device is about 20:1 at best, which is one-hundredth or less of the extinction polarization ratio (3000:1) of a polarizer presently used in a liquid crystal display. Note that herein the ratio in intensity between linearly polarized light rays orthogonal to each other is called the “emission polarization ratio” for the light emitted from an organic EL light emitting device, while the same ratio is called the “extinction polarization ratio” for the light transmitted by a polarizer.
For example, the aforementioned Japanese Laid-Open Patent Publication No. 11-316376 discloses enhancing the degree of alignment of an organic EL layer by means of rubbing, oblique evaporation or mechanical deposition. However, this method fails to provide a sufficiently high emission polarization ratio. Japanese Laid-Open Patent Publication No. 11-204261 discloses a method in which a rubbed alignment film is placed between a light emitting layer and an anode electrode and a liquid crystalline light emitting material is aligned with the alignment film. This method fails to provide a sufficiently high emission polarization ratio, either.
If the emission polarization ratio of a backlight is low, the quality of black display decreases due to light leakage. Therefore, a sufficient contrast ratio will not be obtained without provision of a polarizer on the side of the backlight.
In view of the above problems, a main object of the present invention is providing an organic EL light emitting device having a higher emission polarization ratio than that conventionally obtained, and a liquid crystal display using such an organic EL light emitting device.